Electrolytic refining of copper



Patented June 12, 1951 ELECTROLYTIC REFINING OF COPPER Stanislaus Skowronski, Metuchen, and Merrill A.

Mosher, Woodbridge, N. J assignors to International Smclting and Refining Company, a

corporation of Montana No Drawing. Application January 22, 1949, Serial No. 72,264

5 Claims.

This invention relates to electrolytic refining of copper, and is particularly directed to the provision of an improved combination of addition agents in the electrolyte. In accordance with the invention casein with glue are usedtogether as the addition agents. We have found that with this combination a smaller total amount of addition agents is required than when either glue or casein is used in combination with some third addition agent, and substantially increased current efficiencies are obtained. The combination of glue and casein results in a much more satisfactory cathode deposit than can be obtained when either one is used alone as the addition agent.

In the electrolytic refining of copper, an .electric current is passed between cast anodes of copper to be refined and cathodes of pure electrolytically refined copper, both the anodes and cathodes bein immersed in an electrolyte comprising an aqueous solution of cupric sulfate and sulfuric acid. Under the influence of the electric current .copper is dissolved from the anode into the electrolyte, and is deposited from the electrolyte on to the cathode in purified form. Impurities present in the anode either dissolve in the electrolyte without being redeposited at the cathode, or accumulate in an insoluble anode mud. After the cathode deposit has built up to a substantial thickness (a quarter inch or more), the cathode is removed and melted for castin into marketable shapes.

Regular additions of so-called addition agents are made to the electrolyte during the refining operation. These usually are complex organic compounds, or mixtures of such compounds, which serve to insure the formation of a smooth, dense cathode deposit. If no addition agent is used, the cathode deposit grows very irregularly and develops sprouts or trees which soon 2 latter is melted. The manner in which addition agents function to produce a smooth and dense cathode deposit is not precisely and fully understood, but it is the concensus of opinion that eifective addition agents form positively charged colloidal particles in the electrolyte. Whenever a projection begins to form on the surface of the cathode, the flow current tends to focus on' such projection and the charged particles of the addition agent are caused to migrate to it and collect on it. The resulting accumulation of the addition agent on the projection partially insulates it and so prevents it from growing further.

A great many different materials have been used as addition agents. Unfortunately they often have effects on the quality of the cathode deposit that are not desirable, such as makin it undesirably hard and brittle, and they lead to reduced current efficiencies. A great deal of work has therefore been done to find an addition agent, or combination of addition agents, that gives as smooth a deposit as possible while having a minimum of undesirable effects. Animal glue and caesin individually and in combination with other materials such as Goulac (a lignin pitch product obtained from paper mill Waste) are among the addition agents heretoe fore used. Glue particularly has been used in combination with Goulac in electrolytic copper refining, and this has been perhaps the most satisfactory combination of addition agents heretofore developed for such use. Casein has not been used in electrolytic copper refining, but has been used alone and in combination with still other agents in electroplating operations.

.We have discovered that animal glue and casein, when used together as addition agents, possess unusual advantages in the refining of copper electrolytically; and in fact this new combination is distinctly superior to the combination of glue and Goulac which is perhaps the best combination of addition agents for copper refining heretofore known. Much less glue and casein are required to produce cathodes of good quality when the two are used together than when either is used in combination with other agents such as Goulac. The current efliciency obtained with the glue-casein combination is very markedly superior to that obtained with glue-Goulac and other combinations. The qualtity of the cathode (smoothness and freedom from inclusions of electrolyte) obtained when using the new combination of addition agents is equal if not superior to that obtained with any heretofore-used addition agent or combination, and is very much superior to the deposit resulting from the use of glue or casein alone.

Based on these discoveries, our invention contemplates the improvement, in the electrolytic refining of copper, of establishing and maintaining in the electrolyte both casein and glue in concentrations from 0.001 to 0.003' gram of casein and from 0.0003 to 0.001 gram of animal glue. per liter of electrolyte. For best results the casein to glue concentration ratio ispreferably-about three to one (i. e. the concentration of casein maintained in the electrolyte. is preferablyabout three times the concentration of glue maintained therein), but it is not essential that this ratio be maintained. It is very difficult to determine by analysis these low concentrati'onsofsuchcome' plex organic materials as glue and casein, and accordingly the amount required is perhapszmost easily measured in terms got the amount of cathode copper deposited. In such termsthe invention contemplates the addition of from to 2 ounces of casein andfrom /4 to ounces of animal glue to the electrolyte for each ton of cathode copper deposited. The addition is best made to the electrolyte in the course of its circulating flow through the electrolytic cells and associated circulatory system. For all practical copper refining operations, an addition to the circulatingelectrolyte of from 0.1 to. 0.3 pound of casein and from 0.03.to 0.1 pound of animal glue per 1000 cubic feet of electrolyte per day gives very satisfactory results. I

A preferred embodiment of the inventiontanda. description of the improvedresults obtained by its use is set forth below:

Atypical electrolyticzcopper refinery comprises a largenumber of electrolytic cells: eachof which is in the form of;.a.-tank..holding.aconsiderable number of. cast anodes'of'copper to..be refined ar= ranged alternatel with cathodes ofpure electrolytically refined copper. The anodes and cathe odes. are hung vertically' in ;the .cell-tankand aare spaced apart byonlya few inches. An electrolyte comprising an aqueous solution of cupric sulfate: and sulfuric acid. is zintroduced:continuouslyv into: each cell tank at one end andis'continuouslys withdrawn at the other. The electrolyte fills the tank almostto the tops of theanodes and oath! odes. Although cupric sulfate and sulfuri'c acidare the main ingredients of the electrolyte solution, itgenerally also contains other substances such as a small amount-of sodium chloride added to prevent antimony and bismuthzim'purities from accmumulating in the solution, and soluble compounds of such anode impurities as -arsenic, nickel and iron. The electrolyte flowing-from'the electrolytic cell passes through a circulation system including a sump where make-up amounts of re-- quired reagents (such as addition agents) are added; and'a part-of the electrolyte is continue ously withdrawn for treatment to remove accumulations of arsenic, nickel, etc. The electrolyte is pumped back. agffain from the sump to. the electrolytic cell tank. It is most convenient to add the casein-glue combination of addition. agents contemplated by the invention to. the electrolyte in the sump-tank or well, the addition. agents being. added continuously in an amount calculated to maintain them in desired concentrations in the electrolyte.

Animal glue is quite readily soluble in water and in acid solution, and it is therefore added to the electrolyte by preparing a dilute solution which can be run in measured amount continuously into the circulating electrolyte. Casein is diflicult to dissolve in acid solution, but a very dilute solution can be prepared and run continuously in measured amount into the electrolyte in the sump. The. casein solution is best prepared fresh each day because it tendsz to decompose if allowed to stand long in the acid solution.

The casein solution should be added in such amount as to introduce into the electrolyte from havelobtainedparticularly satisfactory results by adding casein in an amount of 1.2 ounces and glue-in a-n"amount of 0.4 ounce for each ton of copper deposited on the cathodes. In all ordinaryscopper refining operations, optimum results are obtained by the addition of these agents in amounts rangingfrom 0.1120 0.3 pound of casein and. from 0.03 to 0.1 pound of animal glue per.

1000 cubiciee-t of electrolyte per day. lt is-ourpresent preferred practicetoadd about0.l5 pound T of casein and 0.05 poundofanimalglueperl000.- cubic feet of electrolyteper day. Incorporation of-the addition agents. in. the amounts indicatedi are, in general, about rightto maintain a concentration from 0.001 to.0.003 gram per liter of casein. and from 0.0003 to,0.001 gram per liter of animal.v glue in the electrolyte as it circulatesthroughthet electrolytic cells.

Casein aloneas. an addition agent has-a very;

beneficial smoothing ,eifect on the cathode deposit, but it makes the cathodes ratherlhardand brittle, even to the :extentzof showingfinecracks at an early stage in-the growth oflthecathodesl These hard, brittle cathodes are very difiicult to-. handle, and electrolyte withits contained impur-i-- ties penetratesinto the cracks and leads to contamination of the copper when the cathodes are- Goulac as-an addition agent has the:v efiect ofproducing a soft copper deposit but; in:- combination-withcasein, it forms a deposit that isnodular, coarse and bulky-and: in .which=much.

melted.

electrolyte is entrained. When=meltedand .cast

into commercial shapes, electrolytically, refinedv copper. produced with .a casein-Goulac combi-v nation of addition agents shows anexcessi-velyg" high contentlof arsenic andnickel, v.whichisa in-r troduced in: consequence of. theimpure 8180-1 trolyte entrained in the cathodes;

Animal glue. alone as an addition: agent,..1ike

casein alone, produces a hard deposit that I is in-- clined. to bezvery brittle. Furthermore, the glue alone isnot always efiective for preventingheavy;

cathode deposit.

has consisted of. 0.-l5'pound of glue and 0.75

pound of Goulac per. ton of copper-deposited:- Surprisingly enough, although casein ancl glue produce hard, brittle cathodes when either: is.

used alone as the addition agent, in combination in accordance with the invention, they yield a fine-grained, dense but adequately soft; cathode that is easily handled and. the surface of which is smooth and free from any objectionable trees or sprouts. combination of glue and casein is necessary to produce satisfactory cathode copper in anelectrolytic refining operation, but other addition agents may be added in small amounts for the purpose of still further improving the quality of the deposit. For example, we have found that Goulac in the amount of 3 ounces per ton (about 0.2 pound per ton) of cathode copper deposited may be added without detrimental effect and perhaps with some improvement in promoting a soft deposit.

The use of glue and casein together as addition agents in accordance with the invention leads to a number of improvements in operating economy and efiiciency. The magnitude of the improvements is readily apparent from a comparison of this combination with the combination of glue and Goulac that has heretofore been commonly used.

In the first place, the amount of addition agents required is much less when using the casein-glue combination of the invention than when using a combination of glue and Goulac. As previously indicated, excellent results are obtained in accordance with the invention when using 1.2 ounces of casein and 0.4 ounce of glue per ton of deposited cathodes. To obtain comparable results with a glue-Goulac combination, about 2.4 ounces of glue and 12 ounces of Goulac per ton of cathode copper produced is required.

In the second place, a very substantial improvement in current efficiency is obtained by using the glue-casein combination of the invention. As one example of this improvement, the

No addition agent other than the average current efiiciency for one month in a group of copper refining cells operating on a single electrolyte circulation system with a combination of glue and. Goulac as the addition agents averaged 85.2%. In the following month, upon changing the addition agent combination to one of casein and glue in accordance with the invention, but without making any other change, the average current efiiciency increased to 87.5%, an increase of 2.3%. As a further example, another group of cells operating in a different electrolyte circulation system and which for some months had been receiving only casein and glue as the addition agent combination, produced electrolytic copper with an average current efliciency of 91.7% in the same month that the current efiiciency was 85.2% in the group of cells that had been operating on a glue-Goulac combination. Over a six month period, the current efficiencies in four difierent groups of cells, each group of which operated in a separate electrolyte circulation system and each of which received a glue-Goulac combination of addition agents, averaged 85.3%, 87.5%, 88.3% and 88.7%; whereas during the same six month period a fifth group of cells operating in still another electuations in electrolyte temperature, composition,

and rate of circulation, than can be obtained with'heretofore used combinations of addition agents. The casein-glue combination generally is even more effective than the glue-Goulac.

combination for protecting. the cathode deposit from nodular or other objectionable growths. It also. seems to be more persistent in its efiectiveness, in that with cells in cascade arrangement equally good results are obtained in the cells in the lower tiers as in the cells in the upper tiers. With glue-Goulac the cathode deposits are always inferior in the cells of the lower tiers to the cathodes produced in the upper-tier cells (where electrolyte to which the glue-Goulac additions have been freshly made is introduced). The greatly reduced amount of organic matter that is in the electrolyte when using the caseinglue combination results in making the anode mud much less bulky and much easier to handle in treating it for the recovery of gold, silver, and other values, than is the case when using a glue-Goulac combination of additions. It is also easier, with the casein-glue combination, to disperse additions of these reagents in the electrolyte than it is with glue-Goulac, and problems involved in avoiding needleor wirelike growths on the cathodes due to inadequate dissemination of the added reagents throughout the body of the electrolyte are largely overcome.

We claim:

1. In the electrolytic refining of copper, in which an electric current is passed between anodes of copper to be refined and cathodes of pure copper immersed in an electrolyte comprising an aqueous solution of cupric sulfate and sulfuric acid, the improvement which comprises maintaining both casein and animal glue in the electrolyte in concentrations of from 0.001 to 0.003 gram casein and from 0.003 to 0.001 gram of animal glue per liter of electrolyte.

2. In the electrolytic refining of copper, involving passing an electric current between anodes of copper to be refined and cathodes of pure copper immersed in an electrolyte comprising an aqueous solution of cupric sulfate and sulfuric acid, the improvement which comprises adding to said electrolyte from to 2 ounces of casein and from A1 to ounce of animal glue for each ton of copper deposited on the cathodes.

3. In the electrolytic refining of copper, involving passing an electric current between anodes of copper to be refined and cathodes of pure copper immersed in an electrolyte comprising an aqueous solution of cupric sulfate and sulfuric acid, the improvement which comprises adding to said electrolyte about 1.2 ounces of casein and about 0.4 ounce of animal glue for each ton of copper deposited on the cathodes.

4. In the electrolytic refining of copper, involving passing an electric current through a cell having anodes of copper to be refined and cathodes of pure copper immersed in an aqueous electrolyte of cupric sulfate and sulfuric acid, and involving continuous circulation of the electrolyte through said cell, the improvement which comprises continuously adding to said electrolyte in the course of its circulation from 0.1 to 0.3 pound of casein and from 0.03 to 0.1 pound of animal glue per 1000 cubic feet of electrolyte per day.

55:11:11? the' electrolytic 1 -efiningjofh copper; in'.- volvmg-zpassing-anelectric-current:through a. ce11 having:- an'odes of a copper to be refined and" cathodes of pure copper immerseddnan aqueous e1e'c-- trolyteoi cupricisulfate and sulfuric acid, and-imvolvingzcontinuous vcirculation of the electrolyte throughusaid cell, the improvement whichicomper 1000- cubic feet of electrolyte pten day;

STAN ISLAUS SKOWRONSKI; MERRILL A: MOSHERE REFERENCES CITED The following references I are of record. in the Principles of!E}ecti 0p1aipg and Elecjzroform ing iby- WiIIiam -BIu-m and George B. Hogaboom,v

2dEdition,-v1930; pa e-2'16;

Special Volume of The Eiectrochemical Spciety, Modern-- Electfoplating, published" 1942,. page 

1. IN THE ELECTROLYTIC REFINING OF COPPER, IN WHICH AN ELECTRIC CURRENT IS PASSED BETWEEN ANODES OF COPPER TO BE REFINED AND CATHODES OF PURE COPPER IMMERSED IN AN ELECTROLYTE COMPRISING AN AQUEOUS SOLUTION OF CUPRIC SULFATE AND SULFURIC ACID, THE IMPROVEMENT WHICH COMPRISES MAINTAINING BOTH CASEIN AND ANIMAL GLUE IN THE ELECTROLYTE IN CONCENTRATIONS OF FROM 0.001 TO 0.003 GRAM CASEIN AND FROM 0.003 TO 0.001 GRAM OF ANIMAL GLUE PER LITER OF ELECTROLYTE. 